The present invention relates to a printing machine, and more particularly, to the type of printing machine which is provided with a reciprocatingly movable printing table. The printing table is arranged to move from a position in which material to be printed is placed upon the table (hereinafter referred to as the material-insertion position) to a position in which material is printed (hereinafter referred to as the printing position) and back again.
Although the present invention can be applied to any type of printing machine operating in accordance with the above, the following description will be made with reference to a silkscreen printing machine. Such a printing machine has a stencil mounted above the printing table, and a squeegee which is associated with the stencil and which rests against the same during a printing operation, the squeegee being arranged, in the material printing position, to move across the stencil and to press printing ink therethrough to a rigid material carried by the printing table beneath the stencil.
By rigid material is meant here, and in the following, a material which can be lifted by its edge from the printing table and/or a material whose edge can abut a stop during movement of the printing table while permitting an opposite edge of the material to be displaced along the printing table during said movement without the material wrinkling. Such rigid material may comprise such card or board as that is provided by the printing machine during a printing operation with a printed circuit diagram or an insulating layer.
As before mentioned, the printing table shall be able to move between a first position, i.e. a material-insertion position, and a second position, i.e. a printing position. To enable the material to be localised or registered in relation to the printing table and the stencil, together with its pattern, placed above said table, there is provided on the printing table registering means with which the material, and particularly corresponding registering means formed in the material, shall be brought to co-act. In order to obtain exact registry, the registering means (pins) of the printing table and the registering means (holes) of the material shall be caused to co-act with each other. These registering means shall be caused to co-act with one another when the printing table occupies its first position, since when occupying its second position the printing table is located immediately beneath the stencil and other means for printing the material.
Since the orientation of the printing table in its second position is exactly related to the frame and to the pattern on the stencil, registration of the material in the first position relative to the table will be the same as in the second position.
It is known to arrange on the printing table of a printing machine, and particularly, on the printing tables of silkscreen printing machines, fixed peg-like registering means. These registering means shall be caused to co-act with holes disposed in the material to be printed. In this way, the material is positioned exactly relative to the printing table and the patterned stencil arranged thereabove. Such peg-like registering means are primarily used when manufacturing printed circuit cards, although they can, of course, be used for other material to be printed.
When the material is to be printed in limited quantities, it is necessary after a short period of time to change the position of the fixed registering means, in a manner such that their mutual position corresponds to the corresponding registering means in the new material to be printed. This can readily be effected in accordance with the invention, owing to the fact that the registering means are displaceably arranged in grooves but can be secured by means provided therefore in predetermined positions or in any selected position.
It is normal, however, for the groove of the registering means to be open. In such case, however, the pattern will not be transferred to the material with sufficient accuracy, owing to the fact that the material adjacent the groove is bent down by the force exerted thereon by the stencil and the squeegee. Although it has long been desirable to fill the groove between the registering means, those measures hitherto proposed have been much too complicated.
It is also desirable, particularly in the case of printing machines in which only a small number of printing operations is to be carried out, for the actual registering of the registry means, and the registry means, to take place in the first position of the printing table, and for the registry means to be placed in the vicinity of the edge facing the person placing the material onto the table. In this way, the material can be inserted and registered very rapidly and in a manner which can be readily superintended and checked. The material is registered in relation to the printing table by inserting the peg-shaped registering means into holes formed in the material. When the width of the material to be printed allows it, two or more sheets of different material can be placed side by side on the table, and the separate materials provided with different print.